The original passive magnetic bearing, developed by one of the inventors of the present invention and fully described in U.S. Pat. No. 5,302,874, has several advantages over conventional magnetic bearings. The passive magnetic bearing eliminates the need for position sensors, control electronics, and high-power amplifiers. It provides a bearing which is much simpler and less expensive than competing conventional bearings. However, the passive magnetic bearing provides relatively less stiffness when compared to conventional magnetic bearings.
To address this obstacle, the inventor of the passive magnetic bearing has combined the passive magnetic bearings with active components to create a semiactive bearing, which is also fully described in U.S. Pat. No. 5,302,874. While the semiactive magnetic bearing possesses load capacity and stiffness characteristics which are similar to those of conventional active magnetic bearings, the semiactive bearings achieve these characteristics by using expensive and complicated sensors, amplifiers and control systems.